Cancer cachexia is a syndrome of progressive nutritional depletion which causes significant morbidity and mortality in cancer patients. One of the main pathogenetic mechanisms underlying cancer cachexia is a complex interaction between the host and the tumour. Tumour cells interact with host cells within the tumour mass resulting in the production of catabolic mediators which degrade host tissue. In addition, the host may mount an aberrant metabolic response to the tumour. However, in recent years, it has also been understood that patient factors, including age and levels of physical activity, and the specific mechanics of protein metabolism in cancer patients may also have a significant impact. In this review article, we not only summarise previous knowledge surrounding host-tumour interaction, but we also discuss these broader concepts in the pathogenesis of cancer cachexia. Clinicians should consider such concepts in the design of an effective multimodal therapy for cachexia.